1. Field of the Invention
The invention relates to use of the cis-(Z) isomer or isomeric mixtures containing specified ratios of the cis-(Z) and the trans-(E) isomers of doxepin and metabolites of doxepin, as well as pharmaceutically-acceptable salts and prodrugs of the same; and compositions containing the same, for the treatment of sleep disorders.
2. Description of the Related Art
Sleep is essential for health and quality of life. Insomnia is a subjective complaint of dissatisfaction with the quantity, quality or timing of sleep. Insomnia is estimated to occur in approximately 12% to 25% of the general population, although this is probably an underestimate as there is evidence that many adults do not report their sleep problems to a health care professional.
One study has found that fewer than 15% of those who suffer from insomnia are treated with prescription medications. Medications commonly used to treat sleep disorders such as insomnia, include sedative antidepressants, antipsychotics, antihistamines, melatonin receptor agonists, benzodiazepines, and non-benzodiazepine hypnotics.
Benzodiazepines work by binding to and activating sites on the GABA-A receptor complex. Short, intermediate and long-acting benzodiazepines such as triazolam, temazepam and flurazepam were all commonly prescribed for this indication. While these agents have proven to be efficacious and relatively safe, benzodiazepines are associated with a multitude of adverse effects, including residual daytime sedation (“hangover”), amnesia, memory loss and respiratory depression. Rebound insomnia has also been associated with benzodiazepines. Tolerance to the hypnotic effects of the benzodiazepines is common and abrupt discontinuation can result in withdrawal symptoms such as agitation, rebound insomnia, perceptual changes, confusion, disorientation and even seizures.
Non-benzodiazepine hypnotics have become the primary class of medications for the treatment of insomnia. The leading approved non-benzodiazepine insomnia medications, eszopiclone, zolpidem, and zaleplon, also work by binding to and activating the GABA-A receptors. All these drugs approved for the treatment of insomnia that act via the GABA-A receptor, including benzodiazepine and non-benzodiazepine hypnotics, have a potential for addiction and abuse and are classified as Schedule IV controlled substances by the U.S. Drug Enforcement Administration. As a result, many physicians are reluctant to prescribe, and patients are reluctant to take these drugs for chronic use in treating insomnia. The prescribing of a Schedule IV controlled substance brings scrutiny from the Drug Enforcement Administration and other regulatory bodies, and requires registration and administrative controls in physicians' offices.
Also, the sedative antidepressants account for a large percentage of the total prescriptions written for insomnia. The National Disease and Therapeutic Index estimates that more than 60% of the 13 million annual trazodone prescriptions are written for the treatment of insomnia, even though trazodone is not indicated for that usage and has never been promoted for that condition. Although there are very limited data to support the use of trazodone for insomnia and it is associated with undesirable side effects, trazodone is often prescribed because it is a non-scheduled agent, meaning non-addictive, unlike the benzodiazepines and other GABA-receptor agonists which are approved for the treatment of insomnia.
Recently a new hypnotic with a mode of action different from other hypnotics has been introduced. Ramelteon is a melatonin receptor agonist with high affinity for melatonin MT1 and MT2 receptors. It is indicated for sleep onset insomnia but it has not been shown to produce a sleep maintenance benefit. It does not affect the GABA-A receptor complex, is not addicting and is not scheduled.
Therefore, it is desirable to have a pharmacological agent for the treatment of insomnia which is more effective and/or has fewer side effects that those currently used.